The present invention concerns a device, which detects road areas using an imaging means that employs a camera mounted on a vehicle such as an automobile, etc.
In recent years, devices which judge the distance and size of objects in front of the vehicle and appropriately control the vehicle in accordance with this judgment have been proposed for the purpose of improving safety of driving vehicles.
An on-road object recognition apparatus which correctly recognizes objects in front of a vehicle is described in Japanese Patent Application Kokai No. Hei 7-225126 as a device associated with a method which uses an optical distance measuring device consisting of two light-receiving elements and judges whether imaged entities whose distances are detected are physical objects or road areas (including characters or white lines drawn on the road surface). This device is equipped with a stereo camera that images the road surface on which the vehicle is operating. The image obtained by this camera is divided into a plurality of windows, and the distance to the entity that is imaged is calculated for each window. Objects in front of the vehicle are recognized by comparing the distance to this entity that is imaged and a reference distance determined for each row range of the window.
In the device described in Japanese Patent Application Kokai No. Hei 7-225126, entities imaged by the camera are judged to be physical objects or road areas with an assumption that the road surface extends horizontally in front of the vehicle. Accordingly, in case the vehicle is inclined due to pitching or rolling, or in case the area in front of the vehicle is a slope or a bank, physical objects on the road surface may be erroneously judged and identified as road areas. Likewise road areas may be erroneously judged and identified as physical objects.
Accordingly, one object of the present invention is to provide a device which can detect road areas without confusing physical objects and road areas even in case the vehicle is inclined due to pitching or rolling, or in case the road surface on which the vehicle is running is a hill or a bank. Furthermore, another object of the present invention is to provide a device that can detect physical objects on the road surface (including other vehicles and obstructions) on the basis of the road areas that are detected.
A road area judgment system is provided which includes at least one imaging device or an image sensor, and an extraction device that acquires brightness values for a plurality of windows including image areas immediately in front of the vehicle from an image that is captured from the imaging sensor. The image is divided into a plurality of windows. The extraction means extracts a reference brightness value on the basis of the plurality of brightness values. The judgment system includes a judgment device that compares the brightness value of at least one other window with the reference brightness value and judges the other window to belong to a road area if the different is within a predetermined range.
According to the invention, the road surface itself is detected based on brightness rather than the distance to the road surface. Road areas can be determined without confusing physical objects and road areas even in case the vehicle is inclined due to pitching or rolling, or in case the area in front of the vehicle is a slope or a bank because determination does not depend on the distance.
According to another aspect of the invention, the system sets the brightness value of the other window that has newly been determined to be a road area by the judgment device as a new reference brightness value. The new reference brightness value is used for determining the next window. Thus, the reference value is progressively changed to reflect the variation of the brightness of the road according to locations in the whole image. This way, road areas can be determined with greater precision.
According to another aspect of the invention, the road area judgment system has at least two imaging sensors and equipped with measuring device that is installed at a predetermined spacing. The system measures the distance to an object on the basis of two or more images obtained by the two or more imaging sensors. The images areas that have brightness values significantly different from the road areas are judged to belong to a physical object other than the road, such as a car or to belong to a marking provided on the road. The measuring device measures the distance to such an object or to a marking.
According to another aspect of the invention, when a judgment is made that windows belong to a physical object or to a marked area on the road, further analysis is carried out based on the measured distance of such windows and the measured distance of other windows that have been determined to belong to a road area. If the distances match, the windows being studied are judged to belong to a marking on the road. Thus, markings on the road are distinguished from other physical objects such as cars.